Late Precambrian Mafic Dyke Swarms of the Aldan Shield and Their Importance in Ore-Magmatic Processes

МИНИСТЕРСТВО НАУКИ И ВЫСШЕГО ОБРАЗОВАНИЯ РОССИЙСКОЙ ФЕДЕРАЦИИ НАЦИОНАЛЬНЫЙ ИССЛЕДОВАТЕЛЬСКИЙ ТОМСКИЙ ГОСУДАРСТВЕННЫЙ УНИВЕРСИТЕТ

LARGE IGNEOUS PROVINCES THROUGH EARTH HISTORY: MANTLE PLUMES, SUPERCONTINENTS, CLIMATE CHANGE, METALLOGENY AND OIL-GAS, PLANETARY ANALOGUES (LIP – 2019)

Abstract volume of the 7 International Conference Tomsk, Russia, 28 August – 8 September 2019

КРУПНЫЕ ИЗВЕРЖЕННЫЕ ПРОВИНЦИИ В ИСТОРИИ ЗЕМЛИ: МАНТИЙНЫЕ ПЛЮМЫ, СУПЕРКОНТИНЕНТЫ, КЛИМАТИЧЕСКИЕ ИЗМЕНЕНИЯ, МЕТАЛЛОГЕНИЯ, ФОРМИРОВАНИЕ НЕФТИ И ГАЗА, ПЛАНЕТЫ ЗЕМНОЙ ГРУППЫ (КИП – 2019)

Тезисы VII Международной конференции Томск, Россия 28 августа – 8 сентября 2019 LATE PRECAMBRIAN MAFIC DYKE SWARMS OF THE ALDAN SHIELD AND THEIR IMPORTANCE IN ORE-MAGMATIC PROCESSES

Okrugin A. V.1, Ernst R. E.2,3, Beryozkin V. I.1, Popov N. V.4

1 Diamond and Precious Metal Geology Institute (DPMGI), SB RAS, Yakutsk, Russia 2Carleton University, Ottawa, Canada 3 Tomsk State University, Tomsk, Russia 4Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, Novosibirsk, Russia

Keywords: Dyke swarm, basite, mafic magmatism, mantle plume, Aldan Shield

Introduction (Fig.1). The dykes dip steeply (70-90o) showing clear intrusive contacts with the enclosing rocks. Their traceable length varies Integrated petrological-geochemical, geochronologi- from a few to 15 km and the thickness – from several to 200- cal, and ore-mineralogical studies of mafic magmatism are 300 m. The dykes form 200-500 km long and 20-60 km wide of prime importance in reconstructing the formation history swarms crosscutting different terranes. The ENE dyke swarms and metallogeny of ancient platforms (Gladkochub et al., occur mainly in the western part of the Aldan shield where the 2012; Guryanov et al., 2013; Okrugin et al., 2018; Ernst et al., Nirekta (NR), Olondo (OL), Udokan-Tommot (UT), and Kalar- 2016). This paper presents geochemical and age data for the Nimnyr (KN) swarms are identified (Mironyuk et al., 1971). swarms of Late Precambrian unmetamorphosed mafic dykes In the middle part of the Aldan shield, apart from the Timpton- of the Aldan shield, which formed in course of a long evolu- Gynym (TG) swarm there are recognized the Timpton-Algama tion of the Siberian platform following consolidation of the (TA) and the El’kon-Gonam (EG) belts of NW strike (Okrugin ancient basement of the Siberian (North Asian) craton, but are et al., 2000). In the east of the shield, the dykes of the Maimakan overlain by the Phanerozoic sedimentary cover. Complex are grouped into the Uchur-Uyan (UU), South-Uchur (SU), and Ukikan (UK) fields of dyke swarms (Guryanov et al., Results 2013). Mafic dykes are widespread within the Aldan shield that rep- The Precambrian age of the dykes was ear- resents the northern Chara-Aldan domain of the Aldan-Stanovoy lier supported by K-Ar dating (1050-1650 Ma) of superterrane including the West Aldan, Nimnyr, Sutam, Uchur, the rocks (Okrugin et al., 2000). More well-con- and Batomga terranes separated by tectonic mélange zones strained ages were obtained recently from U-Pb dating of zircon and baddeleyite (Ernst et al., 2016), which are shown in Fig.1 with a star (*).

Figure 1. Sketch map of Late Precambrian dyke swarms in the Aldan shield 1 – Siberian platform cover; 2-5 – terranes of the Aldan-Stanovoy shield (after Smelov et al., 2009): 2 – Nimnyr (N) and Chogar (Ch) granite-orthogneiss; 3 – West Aldan (W) and Batomga (B) granite-greenstone; 4 – Sutam (S) and Uchur (U) granite-paragneiss; 5 – Tynda (T) tonalite-trondhjemite-gneiss; 6 – tectonic mélange zones (am - Amga, kl - Kalar, tr - Tyrkanda; 7 – Lower Khani graben- syncline with metagabbro-diabase dykes and sills (Popov et al, 2012); 8 – Chiney layered gabbroic massif; 9 – dyke swarms; 10 – folded complexes of South Siberia.

94 The age of the NE Kalar-Nimnyr belt (1869 Ma) obtained (open symbols connected by dotted lines) are characterized from dating of a dyke of the TG swarm is close to that (1844 Ma) by a lower P2O5 content and a deeper Nb-Ta minimum. of the NE dyke swarm in northern Cisbaikalia, which suggests The age of metagabbro-diabase dykes and sills of the they had a similar origin (Gladkochub et al., 2012). The dates Kuranakh Complex (1863±9 Ma) in the Lower Khani graben- (1754-1759 Ma) of the NW dykes from the TA belt coincide with syncline is identical to that of basic rocks (1867±3 Ma) in the the ages of the SE dyke swarms in the Anabar uplift and the NE Chiney layered massif (Popov et al, 2012). Chay swarm in the Baikal uplift. The swarms are proposed to intersect in the lower Vilyui river area where the center of the Conclusions Timpton plume aged at 1758-1752 Ma was located (Gladkochub The source of magma for the Late Precambrian dyke et al. 2012; Ernst et al., 2016). swarms in the Siberian (North Asian) craton were undepleted The dykes under consideration were not subjected to intraplate plume-type mafic melts. Magma retardation in deep metamorphism. According to the Russian Petrographic Code chambers could have resulted in contamination of the melts by (2008) they belong to basalts (B) and andesite basalts (BA), crustal material, and could also be responsible for a dual behav- more rarely to trachybasalts (TB) and andesites (A) (Fig.2). ior of Ti during fractionation of various Ti-bearing minerals. In terms of mineral and chemical compositions, the dyke Intrusion of significant volumes of mafic material in the rocks are divided into two groups. The first group consists of form of plumes leads to the formation of large igneous prov- the rocks of the differentiated dolerite-diorite series, and the inces with mafic-ultramafic complexes that can host high-grade second one includes dolerites with transition to trachydoler- deposits of platinum-group metals (PGM), Ni, Cu, Cr, rare ele- ites. The dolerite-diorite rocks are characterized by a high SiO 2 ments, etc. Within the limits of the Aldan-Stanovoy shield there content (49-59%), the presence of interstitial quartz-feldspar are present numerous Au-Pt placers with various PGM associa- micropegmatite (up to 10%), and by the appearance of hyper- tions for which the bedrock sources are as yet unknown. sthene. This series exhibits significant variation (0.52-0.86) in the fractionation ratio F = FeO /(FeO +MgO). SiO , K O, tot tot 2 2 Acknowledgements Na2O, P2O5, and TiO2 increase and CaO decreases with the growing fractionation ratio. That behavior of petrogenic ele- This work was carried out as part of the scientific research ments suggests the formation of homogeneous dykes in course of the DPMGI SB RAS, No. 0381-2016-0003 and supported of multiple injections of tholeiite-basalt melts and their differ- by the RFBR project No. 17-05-00390. entiates from deep-seated intermediate magma chambers. The rocks of the second group are marked by a lower SiO2 con- References tent and by higher values of TiO (1.5-3.1%), P O (0.2-0.7%), 2 2 5 1. Gladkochub D.P., Donskaya T.V., Ernst R. et al. (2012) and alkalis, mainly K O, thus corresponding to dolerites and 2 Proterozoic basic magmatism of the Siberian Craton: subalkaline dolerites. Unlike the rocks of the first group, the Main stages and their geodynamic interpretation. subalkaline dolerites exhibit no clear relationship between the Geotectonics 46: 273-284 distribution of petrogenic elements and the fractionation ratio. 2. Guryanov V.A., Perestoronin A.N., Didenko A.N., Peskov A. Yu., Kosynkin A. V. (2013) Late Paleoproterozoic Basic Dykes in the Ulkan-Uchur District, Aldan- Stanovoy Shield. Geotectonics 47: 279–290 3. Mironyuk, E.P., Lyubimov, V.K. and Magnushevsky, E.L. 1971. Geology of the western part of the Aldan shield. Moscow. Nedra, 236. (in Russian). 4. Okrugin, A.V., Koroleva, O.V. and Beryozkin, V.I. 2000. Distribution and specific composition of Riphean basites of the Aldan shield //Petrography on border of centuries. Syktyvkar, pp. 150-153 (in Russian). 5. Okrugin A.V., Yakubovich O.V., Ernst R., Druzhinina Zh.Yu. (2018) Platinum-bearing placers of Siberian platform: mineral associations and their age characteristics as indicators of large igneous provinces manifested. Artic and Subartic natural resources 3: 36-52 6. Popov N.V., Postnikov A.A., Kotov A.B. et al. (2012) Figure 2. 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Nature Geoscience 6: 464-469 islands, but differ from them by the presence of well-defined 9. Sun S.S., McDonough W.F. (1989) Chemical and negative Th-U and Nb-Ta anomalies and a positive Pb peak. isotopic systematic of oceanic basalts. Magmatism in the The low-Ti rocks of the differentiated dolerite-diorite series Ocean Basins 42: 313-345